This invention relates to new and useful improvements in manufacturing preforms for containers, such as plastic bottles, and to preforms and containers per se. More particularly, the invention relates to a preform used to produce a plastic bottle which is recyclable, but preferably non-refillable.
A conventional PET (polyethylene terephthalate) preform (e.g. 12 ounces) is injection molded from PET homopolymer or PET copolymer such that the resulting preform has a center sidewall thickness in the range of 3 to 4 mm and a thickness in the base forming portion in the range of 3 to 4 mm. The length of such a conventional PET preform for a 12 ounce bottle is in the range of 90 to 95 mm, and the injection molded preform has a stretch ratio in the range of at least 9:1, and preferably 9:1 to 12:1.
Conventional containers made of PET resins are often deficient in that such materials may have both insufficient barrier properties and insufficient thermal stability. Reduced barrier properties of a container may adversely affect shelf life of a product provided within the container. In order to improve the barrier properties of a container, multilayer coatings are often provided within the container.
Accordingly, there is a need in the art for containers having improved barrier properties in order to provide for longer shelf life of the product within the container.
U.S. Pat. No. 5,102,705 to Yammoto et al. discloses a bottle made of polyethylene naphthalate resin and formed by stretching a preform so that the stretch index defined as follows is 130 cm or more: ##EQU1##
In contrast to the express teachings of the Yammoto et al. patent, the present invention operates only in the region corresponding to a stretch index of below 130 cm. Thus, the present invention does not have a stretch index of 130 cm or above.